Transition Metals

Front 1

Define "Transition metal"

Back 1

An element that has an incomplete d sub-shell in either its atoms or one or more of its common ions.

Front 2

What are the general properties of transition metals that the incomplete d sub-shell causes?

Back 2

1. Variable oxidation states

2. Can act as catalysts

3. Form complexes with ligands

3. Form coloured complexes and compounds

Front 3

Define "Ligand"

Back 3

A small molecule or ion that has one or more lone pairs of electrons with which it can form co-ordinate bonds to metals.

Front 4

Define "Complex"

Back 4

A metal ion with co-ordinately bonded ligands.

Front 5

Define "Co-ordinate bond"

Back 5

A type of covalent bond formed when both of the shared pair of electrons come from the same atom.

Front 6

Define "Co-ordination number"

Back 6

The number of co-ordinate bonds from ligands to metal ions.

Front 7

Define "Lewis base"

Back 7

Lone pair donor (ligand).

Front 8

Define "Lewis acid"

Back 8

Lone pair acceptor (metal).

Front 9

Define "Unidentate ligand"

Back 9

Ligands that form one co-ordinate bond to a metal ion.

E.g Chloride ions, Hydroxide ions, Water and Ammonia.

Front 10

Define "Bidentate ligand"

Back 10

Ligands that form two co-ordinate bonds to a metal ion.

E.g See photo

-also known as "en" [left]

Front 11

Define "Multidentate ligand"

Back 11

Ligands that form three or more co-ordinate bonds to a metal ion.

E.g EDTA (6 lone pairs) [left]

-Porphyrin (4 lone pairs) in haemoglobin

Front 12

What is this and why is it important?

Back 12

-Haem complex (Planar)

-Fe (II) ion (Co-ord. 6) with one porphyrin ligand

-Forms haemoglobin when 4 co-ordinate bonds are made, and then one oxygen molecule and one globin molecule (complex protein) form the last 2.

-Red pigment in blood, carries oxygen around the body.

-Better ligands can displace (e.g CO:) causing asphyxiation, as they form stronger co-ordinate bonds.

Front 13

What shape would [M(H20)6]2+ be?

Back 13

-Octahedral

-Bond angle: 90º

-Co-ordination #: 8

-Most common

-Most metals form this

Front 14

What shape does a complex with Chloride ion ligands form?

Back 14

-Tetrahedral

-Bond angle: 109.5º

-Co-ordination #: 4

-Occurs in large ligands

-Also ligands that repel

-E.g :Cl-

Front 15

What shape do Ag+ complexes form?

Back 15

-Linear

-Bond angle: 180º

-Co-ordination #: 2

-Occurs in Ag+ complexes.

Front 16

What is this and what is it used for?

Back 16

-Tollen's reagent

-Bond angle: 180º

-Co-ordination number: 2

-Used to distinguish between aldehyde and ketones

-Forms silver mirror of Ag, when reduced by aldehydes.

Front 17

What shape to Pt+ and Ni2+ complexes form?

Back 17

-Square planar

-Bond angle: 90º

-Co-ordination #: 4

-Common in Pt+ and Ni2+ complexes

Front 18

What is this and what is it used for?

Back 18

-Cisplatin

-Bond angle: 90º

-Co-ordination number: 4

-Successful anti-cancer drug

-Binds to DNA molecules, preventing cell replication (prevents "unzipping" and forms co-ord. bonds with N in guanine)

-Optical isomer transplatin is ineffective

Front 19

What are the benefits and risks of Cisplatin?

Back 19

Benefits

-Can be used to successfully prevent replication of cancerous cells, and so save lives

Risks

-Can also damage non-target healthy cells and could cause further complications

-Other risks/side effects associated with chemotherapy

Front 20

Why do transition metals form coloured complexes?

Back 20

-In compounds, d orbitals don't have the same energy

-The gap in energy between the d-orbital corresponds to the energy of visible light

-The electrons absorb visible light to provide energy for promotion (excitation) of electrons to higher energy levels (d-d transitions)

-∆E=hv

-When different frequencies of light are absorbed, different coloured complexes are made.

Front 21

How can the absorption of different frequencies be used to identify concentrations of ions in solution?

Back 21

A colorimeter can be used to determine the concentration of a coloured complex in solution, as the more intense the colour, the higher the concentration. To calculate this, the colorimeter must be calibrated. The type of ion can be identified by its colour and through chemical tests.

Front 22

What can cause a colour change in a transition metal complex?

Back 22

-Change in oxidation number/state

-Change in ligand

-Change in co-ordination number

Front 23

Which two transition metal elements are common in redox titrations?

Back 23

Manganese (Mn) and Chromium (Cr)

Front 24

What are the colours of Manganese's common oxidation states?

Back 24

Mn (II) ~ Colourless/ very pale pink

Mn (VI) ~Green

Mn (VII) ~ Violet

Front 25

What are the colours of Chromium's common oxidation states/species?

Back 25

Cr (II) ~ Blue (Hexa-aqua 2+ easily oxidised)

Cr (III) ~ Green (Hexa-aqua 3+)

Cr (VI) ~ Orange (Dichromate)

Cr (VI) ~ Yellow (Chromate)

Front 26

What is the redox equation for the titration of Potassium Permanganate (strong oxidising agent) against Iron (II) solution?

Back 26

Front 27

What is the redox equation for the titration of Potassium Dichromate (strong oxidising agent) against Iron (II) solution?

Back 27

Front 28

What is a catalyst?

Back 28

A catalyst is a substance that increase the rate of a reaction by providing an alternative route/mechanism with a lower activation energy. The catalyst is not used up in a reaction.

Front 29

How does a catalyst affect an equilibrium?

Back 29

It only increases the rate at which the equilibrium is reached, it does not alter its position.

Front 30

What is a catalyst that slows down a reaction called?

Back 30

An inhibitor, or negative catalyst.

Front 31

What makes transition metals good catalysts?

Back 31

Variable oxidation states

Front 32

What is a heterogenous catalyst?

Back 32

A catalyst that is in a different phase/state to the reactants. The catalyst is usually a solid, and the reaction takes place on its surface.

Front 33

What are 3 examples of industrial processes that involve heterogenous catalysts?

Back 33

1. Haber process~Fe Catalyst

2. Contact process~Vanadium oxide catalyst

3. Manufacture of methanol from carbon monoxide and hydrogen~Chromium (III) oxide catalyst

Front 34

What are the Vanadium catalysed reactions of the contact process?

Back 34

Front 35

How do heterogenous catalysts work?

Back 35

-At least one reactant adsorbed onto surface (forms bond with solid)

-The places where they adsorb are active sites

-Molecules can move to different sites on effective catalysts

Front 36

How do heterogenous catalysts increase the rate of reaction?

Back 36

-Brings reactants closer together

-Weakens bonds in reactants

-Positions reactants in favourable orientation

Front 37

What are the problems with too much/too little adsorption?

Back 37

Too weak~Not many molecule adsorbed, so little effect

Too strong~Molecules cannot move between active sites, so remain adsorbed and don't meet other reactants

Good catalysts are a fine balance of the two

Front 38

How can catalysts be used more effectively?

Back 38

Maximise their surface area, e.g by using a honeycomb structure. This reduces the quantity needed and so the cost.

Front 39

What is catalytic poisoning and why is it bad?

Back 39

When reactants adsorb too strongly to active sites and block them. They are very difficult to remove. This reduces the number of active sites, and so reduces the efficiency of the catalyst.

Front 40

What are some examples of catalytic poisoning?

Back 40

Lead poisoning of catalytic converters in cars. Blocks sites on Pt and Rh with lead from leaded petrol.

Sulphur poisoning of Fe in the Haber process. Hydrogen gas is contaminated by S (gives it smell to make leaks easier to detect)

Front 41

What is a homogenous catalyst?

Back 41

A catalyst that is in the same phase as the reactants. Most take place in solution.

Front 42

How do homogenous catalysts increase the rate of reaction?

Back 42

The reactions proceed via an intermediate species formed from a reactant and a catalyst, which then reacts further and regenerates the catalyst.

Front 43

What is the equation for the reaction between iodide and peroxodisulphate ions? Why is it slow without a catalyst?

Back 43

Reaction between 2 negative ions without Fe (II) ion catalyst, so otherwise very slow.

Fe (II) a good catalyst because it can be quickly oxidised to Fe (III) ions. Either can be used, as the stages just swap.

Front 44

What is as autocatalysis reaction?

Back 44

A reaction that forms its own catalyst. They are very slow to begin with but increase quickly (until the reactants start to run out).

Front 45

What is an example of an autocatalysis reaction?

Back 45